Second - harmonic generation of ultra-high intensity femtosecond pulses with a KDP crystal

Efficient second-harmonic generation of a high-energy, femtosecond laser pulse in a lithium triborate crystal

We demonstrate the highest efficiency (∼80%) second harmonic generation of joule level, 27 fs, high-contrast pulses in a type-I lithium triborate (LBO) crystal. In comparison, potassium dihydrogen phosphate gives a maximum efficiency of 26%. LBO thus offers high-intensity (>10^18-19W/cm²), ultra-high contrast femtosecond pulses, which have great potential for high energy density science and applications, particularly with nanostructured targets.

Photon Acceleration in a Flying Focus

A high-intensity laser pulse propagating through a medium triggers an ionization front that can accelerate and frequency upshift the photons of a second pulse. The maximum upshift is ultimately limited by the accelerated photons outpacing the ionization front or the ionizing pulse refracting from the plasma. Here, we apply the flying focus-a moving focal point resulting from a chirped laser pulse focused by a chromatic lens-to overcome these limitations. Theory and simulations demonstrate that the ionization front produced by a flying focus can frequency upshift an ultrashort optical pulse to the extreme ultraviolet over a centimeter of propagation. An analytic model of the upshift predicts that this scheme could be scaled to a novel tabletop source of spatially coherent x rays.

High-efficiency broadband second harmonic generation in single hexagonal GaAs nanowire

In this paper, we investigate second harmonic generation in a single hexagonal GaAs nanowire. An excellent frequency converter based on this nanowire excited using a femtosecond laser is demonstrated to operate over a range from 730 nm to 1960 nm, which is wider than previously reported ranges for nanowires in the literature. The converter always operates with a high conversion efficiency of ~10^-5 W^-1 which is ~10³ times higher than that obtained from the surface of bulk GaAs. This nanoscale nolinear optical converter that simultaneously owns high efficiency and broad bandwidth may open a new way for application in imaging, bio-sensing and on-chip all-optical signal processing operations.

Cascaded third-harmonic generation with one KDP crystal

For KH₂PO₄ (KDP) crystal, the phase-matching directions of type-II second-harmonic generation (SHG) and type-II third-harmonic generation (THG) for 1 μm lasers are almost identical, i.e., at (θ=60°, φ=0°) around. Utilizing this special property, we designed a THG converter based on one KDP crystal. A quarter-wave (λ/4) plate was used to adjust the polarization of the SHG wave, and a round-trip optical path was used to realize the SHG and THG procedures successively. When the fundamental light source was a 1064 nm, 40 ps pulse laser, the maximum THG output at 355 nm was 1.13 mJ, and the highest THG conversion efficiency was 30.7%. To the best of our knowledge, this is the first time that the cascaded frequency upconversion processes are realized in one bulk nonlinear optical crystal. This method possesses many advantages for future applications, including high efficiency, a wide-working waveband, low cost, and applicability to many other crystals such as DKDP, ADP, DADP, and Gd_xY_1-xCOB.

Heat coupled Gaussian continuous-wave double-pass type-II second harmonic generation: inclusion of thermally induced phase mismatching and thermal lensing

A model describing the thermal effects in type II second harmonic generation (SHG) of Gaussian continuous-wave (CW) in a double-pass cavity is presented. The thermally induced phase mismatching (TIPM) along with thermal lensing was included in the classical SHG formalism through the interposing the heat and TIPM equations. To this end, eight equations were coupled together and solved simultaneously to reveal how the SHG is affected in time when heat is generated in the crystal. The model showed an excellent agreement with experimental data [Opt. Laser Tech.34, 333-336 (2002)]. Furthermore, a numerical procedure, which was developed in this work, is introduced for simultaneously solving the SHG, heat, and TIPM equations with home-used computing machines.

Ultrahigh contrast from a frequency-doubled chirped-pulse-amplification beamline

This paper describes frequency-doubled operation of a high-energy chirped-pulse-amplification beamline. Efficient type-I second-harmonic generation was achieved using a 3 mm thick 320 mm aperture KDP crystal. Shots were fired at a range of energies achieving more than 100 J in a subpicosecond, 527 nm laser pulse with a power contrast of 10(14).

Energy-scalable temporal cleaning device for femtosecond laser pulses based on cross-polarized wave generation

We report on a compact energy-scalable device for generating high-fidelity femtosecond laser pulses based on spatial filtering through a hollow-core fiber followed by a nonlinear crystal for cross-polarized wave (XPW) generation. This versatile device is suited for temporal pulse cleaning over a wide range of input energies (from 0.1 to >10 mJ) and is successfully qualified on different ultrafast laser systems. Full characterization of the XPW output is presented. In particular, we demonstrate the generation of 1.6 mJ energy pulses starting from 11 mJ input pulse energy. The temporal contrast of the pulses is enhanced by more than 4 orders of magnitude. In addition, pulse shortening from 40 fs down to 15 fs Fourier-transform limit yields an overall peak-power transmission of up to 50%. This device not only serves as an integrated pulse contrast filter inside an ultrafast laser amplifier but also as a simple back-end solution for temporal post-compression of amplified pulses.

Generation of subterawatt sub-10-fs blue pulses at 1-5 kHz by broadband frequency doubling

Blue pulses with durations of 8.5 fs are generated by broadband frequency doubling of subterawatt Ti:sapphire laser systems at 1-5-kHz repetition rates. The average powers are 1.6 W at 5 kHz and 1.9 W at 1 kHz. The peak power is 0.16 TW with a duration of 12 fs at 1 kHz.